Tapply: Apply a Function to a Variable Within Factor Levels

Description

Applies a function, typically to compute a single statistic, like a mean, median, or standard deviation, within levels of a factor or within combinations of levels of two or more factors to produce a table of statistics. This function provides a formula interface to the standard R tapply function.

Usage

Tapply(formula, fun, data, na.action = na.pass, ..., targs = list())

Arguments

formula

a two-sided formula of the form variable ~ factor.1 + factor.2 + ... + factor.n or, equivalently, variable ~ factor.1*factor.2* ... *factor.n. The variables on the right-hand side of the formula are normally factors or are otherwise coerced to factors.

fun

a function, like mean, median, or sd, that takes a vector first argument and typically returns a single number as its value.

data

an optional data frame within which to find the variable and factor(s).

na.action

a function to handle missing values, as in statistical modeling functions like lm; the default is na.pass.

…

arguments to pass to the function given in the fun argument, such as (commonly) na.rm=TRUE.

targs

a list of optional arguments to pass to tapply.

Value

The object returned by tapply, typically simply printed.

Details

The function given by fun is applied to the values of the left-hand-side variable in formula within (combination of) levels of the factor(s) given in the right-hand side of formula, producing a table of statistics.

References

Fox, J. and Weisberg, S. (2019) An R Companion to Applied Regression, Third Edition. Sage.

Examples

Run this code

# NOT RUN {
Tapply(conformity ~ partner.status + fcategory, mean, data=Moore)
Tapply(conformity ~ partner.status + fcategory, mean, data=Moore, 
    trim=0.2)

Moore[1, 2] <- NA
Tapply(conformity ~ partner.status + fcategory, mean, data=Moore)
Tapply(conformity ~ partner.status + fcategory, mean, data=Moore, 
  na.rm=TRUE)
Tapply(conformity ~ partner.status + fcategory, mean, data=Moore, 
  na.action=na.omit)  # equivalent
remove("Moore")
# }

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